1. Field of the Invention
The invention relates to abrasive blasting machines of the type having a runnerhead to which a plurality of radially extending vanes are secured and, more particularly, to a technique for locking the vanes to the runnerhead.
2. Description of the Prior Art
In abrasive blasting machines of the type having a runnerhead to which a plurality of radially extending vanes are secured, it is important to be able to retain the vanes in place under all operating conditions while, at the same time, being able to remove and replace worn or broken vanes with minimal effort. Prior techniques for retaining vanes in the runnerhead have presented various difficulties. For example, vanes have been secured to a runnerhead by bolting the vanes to the runnerhead. This technique makes the vane replacement process time-consuming, and it requires that threaded openings be formed in the runnerhead. In another construction, double runnerheads are provided and the vanes are slid into slots in the double runnerheads from the center of the wheel. The vanes are held in place by a spacer bar which extends between, and supports, the runnerheads. This arrangement requires removal of all feed parts as well as removal of the vanes through the centrally disposed feed spout opening.
Another technique is shown by U.S. Pat. No. 3,383,804, to J. V. Haider. In the U.S. Pat. No. 3,383,804 patent, the vanes are slid into radially extending channels from the periphery of the runnerhead and moved to an extreme innermost position. Retainer pins then are fitted into openings formed in the outer portion of the runnerhead. The retainer pins are disposed perpendicular to the face of the runnerhead. Thereafter, the vanes are slid radially outwardly until the pins are contacted. A locking ring is attached to the center of the runnerhead in order to prevent the vanes from moving radially inwardly so as to possibly free the retainer pins. The retainer pins also are secured in place within the openings in the runnerhead by means of magnets glued in place in the openings. Although this approach is reasonably effective, it requires that the locking ring be removed in order for any given vane to be replaced. Unfortunately, when the locking ring is removed, all of the vanes are freed for movement, thereby making the vane replacement process more difficult. Additionally, the openings formed in the runnerhead for receiving the pins and magnets are quite deep, making the runnerhead manufacturing process more difficult.
U.S. Pat. Nos. 4,402,163; 4,471,583; and 4,509,300, to J. H. Carpenter et al. (hereafter referred to as the Vane Retention Patents), the disclosures of which are incorporated herein by reference, disclose vane retention techniques that overcome most of the objections noted earlier. In the Vane Retention Patents, the runnerhead is provided with a relatively small well, or slot, in each of the channels in which vanes are disposed. The slots are located quite close to the periphery of the runnerhead such that the slots are accessible from the periphery of the runnerhead. The base of the vanes is configured such that a retaining pin can be fitted into the slot in the runnerhead and held in place there upon radially outward movement of the vanes. In order to remove the retaining pin, the vanes are moved radially inwardly a small amount, whereupon the pin can be tilted about 20 degrees and pulled from the slot. This technique makes it easy to replace worn or broken vanes.
Despite the advances made by the Vane Retention Patents, certain problems have not been addressed. That portion of the base of the vane that engages the retianing pin has to be made to close tolerances, or the pin can rotate sidewise and come out of the slot into which it was inserted. Additionally, if the installer does not pull the vanes radially outwardly as part of the installation process, the pin may rotate sidewise and come out of its slot. In order to provide the required dimensional accuracy for the vane base, the casting process used to manufacture the vanes is made more difficult. Specifically, it is necessary to use cores (usually ceramic cores) to manufacture the vanes, and the use of such cores increases the cost of manufacturing the vanes. The use of cores also reduces the number of vane impressions that can be put on a pattern board. For example, with cores, a typical pattern board can hold twelve impressions, whereas without cores, fifteen impressions can be held. Because thousands of vanes are manufactured yearly, the use of cores is an important factor in the cost of manufacturing the vanes.